This invention relates to inlets for tanks, and more particularly vented inlets for tanks filled from pressurized tankers.
Tanks are often filled with liquid from truck tankers by pressurizing the head space above the liquid within the tanker with compressed air to force the tanker contents into the receiving tank. This is most typically done when the liquid being transferred is a corrosive chemical which would damage a pump. Although such a procedure eliminates the need for a pump, a possibility does exist that the pressurized air within the tanker will follow the liquid into the receiving tank and destroy the tank due to excessive pressure.
Generally speaking, the tanker is connected to the receiving tank by a hose, and the compressed air pushing down on the liquid contents forces the liquid through the hose and into the receiving tank. The frictional resistance offered by the hose and fittings limits the maximum velocity of the liquid moving through the hose to a reasonable value. The air displaced by the liquid entering the tank escapes through the normal vent provided on the tank.
However, when the last of the liquid passes through the hose, the compressed air within the tanker rushes through the hose at an extremely high velocity because this air does not meet significant frictional resistance within the hose as the liquid does. This air enters the head space in the receiving tank and expands with almost explosive speed and force. The conventional tank vent cannot relieve this excessive pressure within the tank. When the pressure within the receiving tank exceeds that for which the tank is designed, either the tank head blows off or some other portion of the tank ruptures.
Preferably, the person operating the tanker will interrupt the liquid flow before the last of the liquid leaves the tanker, preventing the compressed air from entering the tank. However, through inattention or carelessness, the operator will occasionally forget to interrupt the liquid at the appropriate time.
Typically, the only prior art solution to the problem is to install a plurality of, or larger, conventional vents on the tank to handle this compressed air. However, these vents increase both the complexity and cost of the tank and do not prevent the compressed air from entering the tank.